ADL5511 Application Help

We got an evaluation board a few days ago and I want to hook it up with optimal part selection to test on our system. The application is to measure the output of an RF amplifier as accurately as possible. Unfortunately some information is missing for the application sheet at this point so I would like to request assistance to fill in those gaps.

Our amplifier outputs a signal at 480KHz which is modulated at different freq. Between 1KHz and 30KHz, the modulation we do is phase change, on a scope this looks very much like AM modulation (100% range).

My end goal is to measure the RMS of this signal with a 50 Ohm input. Can you please direct me to formulas for the filter calculations and the integration capacitor at the output.

The on-chip rms filtering corner is internally set by a 400 Ω resistor and a 20 pF capacitor, yielding a corner frequency of approximately 20 MHz (1/(2xPIx400x20pF) . The internal capacitance can (and generally should) be augmented by connecting an external capacitor between FLT4 (Pin 14) pin to VPOS (Pin 15). This will decrease the filtering bw to (1/(2xPIx400x(20pF+CFLT4)).

In general, the rms rms averaging corner frequency should be set to be significantly less than the bandwidth of the signal. For example, it was experimnetally determined that a 20 MHz LTE carrier requires a minimum filter capacitance of approximately 100 nF to yield a correct rms computation (Corner Frequency is approx 4 KHz).